solubilization of poorly water soluble drug using mixed ... · and rajesh kumar maheshwari2 1school...

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*Corresponding author: Email: [email protected];

British Journal of Pharmaceutical Research4(5): 549-568, 2014

SCIENCEDOMAIN internationalwww.sciencedomain.org

Solubilization of Poorly Water Soluble DrugUsing Mixed Solvency Approach for

Aqueous Injection

Love Kumar Soni1*, Shailendra Singh Solanki1

and Rajesh Kumar Maheshwari2

1School of Pharmacy, Devi Ahilya Vishwavidyalaya, UTD, Takshashila Campus, Indore452001, India.

2Department of Pharmacy, SGSITS, Park Road, Indore 452003, India.

Authors’ contributions

This work was carried out in collaboration between all authors. All authors read andapproved the final manuscript

Received 31st March 2013Accepted 14th September 2013

Published 3rd January 2014

ABSTRACT

Aim: 1) To increase water solubility of indomethacin drug using mixed solvency approach.2) To employ use of non toxic solubilizers for increasing solubility of a poorly water

soluble drug.Study Design: Trial and error based experimental study.Place and Duration of Study: School of Pharmacy, Devi Ahilya Vishwavidyalaya, UTD,Takshashila Campus, Indore, India and College of Pharmacy, IPS Academy, Indore, Indiabetween Jan. 2011 and June. 2012.Methodology: By making mixed solvent (40%) blends of selected water solublesubstances from the hydrotropes (urea, sodium benzoate, sodium citrate, nicotinamide);water-soluble solids (PEG- 4000, PEG-6000); and co-solvents (propylene glycol,glycerine, PEG-200, PEG-400, PEG 600) solubility studies were performed withindomethacin (model drug). On the basis of solubility studies formulation was developed.The solubilized drug and prepared formulation were characterized by ultraviolet andinfrared techniques. Various properties of solution such as pH, viscosity, specific gravity andsurface tension were studied. The developed formulation was studied for physical andchemical stability.

Original Research Article

British Journal of Pharmaceutical Research, 4(5): 549-568, 2014

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Result: Aqueous solubility of drug in case of selected blends ranged from 14.55 mg/ml –19.96 mg/ml (as compared to the solubility in distilled water 0.0464 ± 0.007 mg/ml). Theenhancement in the solubility of drug in a mixed solvent containing 10% sodium benzoate,5% sodium citrate and 25 % S cosolvent (25% S cosolvent contains PEG200, PEG 400,PEG600, Glycerine and Propylene glycol) was more than 400 fold. Prepared formulationF10 show appreciable physical and chemical stability.Conclusion: The results of this study provide guidance for developing an injectableproduct and strategies for improving solubility as well as stability of poorly water solubledrug using the concept of mixed solvency. The proposed technique is economical,convenient and safe. The application of mixed solvency approach in the development offormulations shall prove a boon for pharmaceutical industries.

Keywords: Solubility; Indomethacin; aqueous injection; mixed solvency; nsaids;polyethylene glycol; sodium citrate.

1. INTRODUCTION

The formulation of solutions presents many technical problems to the industrial pharmacist.A growing number of new therapeutic molecules are limited by low or erratic bioavailabilitydue to poor water solubility. Because of the clinical demand for new and more efficaciousanti-cancer, antiviral, and anti-infective drugs, many of these new drugs may be formulatedfor injection. A large percentage of drugs currently in preclinical and clinical development forinjectable administration are considered poorly water soluble. Developing an injectableformulation and drug product for poorly water soluble compound can be challenging becausethere is no one best approach [1-4].

Special techniques are required to solubilize poorly water-soluble drugs. Solubility of drugcan be increased by variety of contemporary methods such as hydrotropic solubilization,solid dispersions, inclusion complex formation, altering the pH and using cosolvents butexcess amount of these agents may have adverse effects. The term “hydrotropy” have beenused to designate the increase in aqueous solubility of various poorly water-solublecompounds due to the presence of a large amount of additives. Concentrated aqueoushydrotropic solutions of urea, nicotinamide, sodium benzoate, sodium salicylate, sodiumacetate and sodium citrate have been observed to enhance the aqueous solubility of manypoorly water-soluble drugs [5-9].

The solubility of weak electrolytes and non polar molecules can be increased by the additionof water miscible solvent in which the drug has good solubility. This process is known as“Cosolvency”. It is proposed that the cosolvent system work by reducing the interfacialtension between predominantly aqueous solution and hydrophobic solute [10].

Cosolvent solubilization is particularly important for parenteral dosage form where it isdesirable to incorporate the required dose as true solution in the smallest possible volume ofliquid. Hydrotropes and cosolvents are used in 13% of FDA approved parenteral products.[11-13].

Poorly soluble drugs usually possess hydrophilic-hydrophobic balance favorable to theirpermeation through GI membranes so that dissolution becomes the decisive factor in thebioavailability of drugs. Solubilization of insoluble drugs has been extensively studied to


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overcome difficulties encountered during pharmaceutical formulation. Most commonly usedexcipients to improve the solubility of a non polar drug in aqueous media are buffers,hydrotropes, surfactants, cosolvents and complexing agents. These can be used eitheralone or in combination. Recently, the synergism of two or three techniques has drawnparticular interest [14-16].

Based on large number of experiments on solubilization of poorly water-soluble drugs,authors are of the opinion that hydrotropy is another type of cosolvency technique and allwater soluble substances whether solids, liquids or gases have solubilizing properties.Maheshwari et al. have shown application of hydrotropy and mixed hydrotropy in titrimetricand spectrophotometric estimations of a large number of poorly water-soluble drugsprecluding the use of organic solvents [17-19]. Melted (temperature less than 100ºC) Poly-ethylene glycol (PEG)-4000, PEG-6000 and PEG-8000 dissolves diclofenac sodium (meltingpoint: 283ºC), thus, acting as solvent for the drug [20]. Melted urea (M.P.: 132-135ºC)dissolves diclofenac sodium (M.P.: 283ºC). Melted ibuprofen (M.P.: 78ºC) dissolvesdiclofenac sodium (M.P.: 283ºC), salicylic acid (M.P.: 159ºC) and niacinamide (M.P.: 132ºC),which again shows that melted ibuprofen acts as solvent for diclofenac sodium, salicylic acidand niacinamide, respectively. In supercritical fluid technology, liquefied carbon dioxide actsas solvent for many insoluble substances. These points indicate that all types of substancespossess some solvent character [20-21].

This mixed solvency concept may be utilized to prepare concentrated (say 40% w/v or so, instrength) combined aqueous solutions of various water-soluble additives from the categoriesof so called, hydrotropes (sodium benzoate, sodium ascorbate, sodium citrate, niacinamide,urea), co-solvents (glycerin, propylene glycol, ethanol, PEG 200, 300, 400, 600), watersoluble solids (PVP, PEG 4000, 6000, 8000,), and cyclodextrins (beta cyclodextrin, HP betacyclodextrin). These are employed in small and safe concentration to solubilize poorly watersoluble drugs to be developed into suitable dosage forms (solutions, syrups, injections,topical solutions etc). The authors propose mixed solvency approach for poorly water solubledrugs (Fig. 1).

In the present investigation, the poorly water-soluble drug indomethacin is selected as modeldrug for formulating aqueous injection using mixed solvency approach [22-27]. Indomethacinis an acidic non-steroidal anti-inflammatory agent. It is a non-selective inhibitor of cyclo-oxygenase (COX) 1 and 2 enzyme that participates in prostaglandin synthesis fromarachidonic acid. Indomethacin is a white to pale yellow crystalline powder with almost noodor. it is water insoluble in nature [28-29].

The poor aqueous solubility and wettability of the drug give rise to difficulties in formulationof parenteral solutions and may lead to a variable bioavailability. The present study wasaimed to investigate the effect of mixed solvent system on the solubility of indomethacin, andto attempt formulation as aqueous injection. The feasibility of preparing injection wasexamined, suitable blend with good solubility profile selected and parenteral dosage formwas formulated. Investigations related to chemical interaction were done by UVspectrophotometery and by Fourier transform infrared spectroscopy. Finally, the short-termphysical and chemical stability study was conducted.


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Fig. 1. Structure of Indomethacin and water soluble agents used for mixed solvency

2. MATERIALS AND METHODS

2.1 Materials

Indomethacin was obtained as gift sample from Neon Laboratories, Mumbai, India.Nicotinamide and Propylene glycol were purchased from Loba Chemie, Mumbai. Sodiumbenzoate, Urea, Sodium citrate, Glycerin, PEG 200, PEG 400, PEG 600 and PEG 6000were obtained from Merck Chemicals Limited, Mumbai, India. All other chemicals andsolvents used were of analytical/HPLC grade.

2.2 Experimental

2.2.1 Estimation of indomethacin

The calibration curve of indomethacin was prepared in distilled water and variousconcentrations of water soluble agents (hydrotropic agents and co-solvents) and estimatedat 320 nm using double-beam UV-Vis spectrophotometer (UV-1800, Shimadzu, Japan) [17-20,26].

2.2.2 Solubility determination

Solubility of indomethacin in various solutions was determined by equilibrium solubilitymethod. Excess amount of drug was added to 5 ml screw-capped glass vials containingbuffers of pH (1.2 -10.0), aqueous solution of hydrotropic agents and different concentrationof solubilizers (Table 1 and 2). The vials were shaken for 12 hr on mechanical shaker (LabHosp, Mumbai, India) at room temperature. The solutions were allowed to equilibrate for the


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next 24 hr. The solution was transferred into eppendorf tubes and centrifuged for 5 min at2000 rpm. Supernatants of each vial was filtered through 0.45µ membrane filter (PallCorporation, USA) and analyzed for drug content spectrophotometrically at 320nm aftersuitable dilutions. The study was performed in triplicate [10, 22-26].

Table 1. pH dependent solubility of indomethacin at room temperature

Buffer Solutions Solubility* (mg/ml) Enhancement RatioDistilled Water 0.0464 ±0.007 −Hydrochloric acid buffer pH 1.2 0.0121±0.004 0.260Hydrochloric acid buffer pH 2.2 0.0138±0.011 0.297Acid phthalate buffer pH 4.0 0.360 ± 0.014 7.758Phosphate buffer pH 5.8 0.461 ± 0.009 9.935Phosphate buffer pH 8.0 1.911 ± 0.007 41.18Alkaline borate buffer pH 9.0 2.660 ±0.012 57.32Alkaline borate buffer pH 10.0 3.768 ±0.006 81.20

* Average of 3 determinations

Table 2. Solubility enhancement ratio of indomethacin in Different solubilizers at roomtemperature

Solvents Solubility* (mg/ml) Enhancement RatioDistilled water 0.0464±0.007 --20 % Sodium Benzoate 17.226±0.011 371.2540 % Sodium Benzoate 30.857±0.008 665.02120 % Urea 3.883±0.005 83.68540 % Urea 8.632±0.014 186.03420 % Nicotinamide 14.216±0.017 306.37940 % Nicotinamide 26.418±0.006 569.35320 % Sodium Citrate 0.316±0.012 6.81040 % Sodium Citrate 0.704±0.016 15.17220 % w/v Propylene Glycol 0.198±0.014 4.2640 % w/v Propylene Glycol 0.546±0.008 11.76720 % w/v Glycerine 0.442±0.004 9.52540 % w/v Glycerine 1.147±0.006 24.71920 % w/v PEG 6000 0.548±0.009 11.81040 % w/v PEG 6000 1.230±0.015 26.50820 % w/v PEG 200 0.412±0.016 8.87940 % w/v PEG 200 1.029±0.004 22.17620 % w/v PEG 400 0.497±0.009 10.71140 % w/v PEG 400 1.203±0.007 25.92620 % w/v PEG 600 0.612±0.010 13.18940 % w/v PEG 600 1.522±0.014 32.801


2.2.3 Influence of pH on solubility and stability

Samples of saturated solution of drug were kept at different pH for 30 days and analyzed forthe drug content at 1, 7, 14 and 30th day to obtain the % of degradation and thereby to findthe pH of maximum stability of indomethacin [22-26].


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2.2.4 Method of determination for additive/synergistic effect on solubility in blends

An equilibrium solubility method was used to determine the additive or synergistic effect onsolubility. The total strength of all solubilizers was 40% w/v (constant) in all aqueous mixedsolvent systems (Table 3). The solubility of indomethacin was determined in these systems[20-21,26].

Table 3. Mixed solvent (total concentration 40%, constant) for saturated solubilitydetermination of indomethacin

Blend Code Solvents Solubility* (mg/ml) Enhancement RatioA1 Distill water 0.0464±0.007 ----F1 15% SB+25% S 5.698± 0.007 122.801F2 15 %UR+25% S 1.507±0.011 32.478F3 15%N+25% S 2.279±0.008 49.116F4 15% SC+25% S 10.588±0.006 228.189F5 10%SB+5%UR+25% S 8.235±0.012 177.478F6 10%UR+5%N+25% S 5.073±0.009 109.331F7 10%N+5%SC+25% S 14.558±0.007 313.750F8 10%SC+5%SB+25% S 17.867±0.004 385.064F9 10%SB+5%N+25% S 12.205±0.009 263.038F10 10%SB+5%SC+25% S 19.963±0.007 430.237F11 10%N+5%UR+25% S 15.330±0.011 330.387F12 10%N+5%SB+25% S 16.029±0.014 345.452

* Average of 3 determinationsSB- Sodium benzoate, UR- Urea, N- Nicotinamide, SC- Sodium citrate, S- Solvent system containing

5% of each PEG 200, PEG 400, PEG 600, Glycerin and Propylene glycol

2.2.5 Properties of mixed solvent solutions

The solution properties of mixed solvents such as pH, viscosity, specific gravity and surfacetension were studied using digital pH meter, Brookfield viscometer, pycnometer andstalagmometer respectively (Table 4) [22-26].

Table 4. Properties of the optimized blends

ExperimentBlends

pH Viscosity(cps)

Surface tension(dynes/cm)

Specific gravity

F7 7.51 6.04 54.22 1.054F8 7.19 6.15 55.84 1.012F10 7.08 6.12 59.24 1.008F11 6.94 6.14 55.38 1.049F12 7.13 6.09 56.42 1.044

2.2.6 Drug excipient compatibility studies

2.2.6.1 UV spectral studies

To study the possible spectroscopic changes in the structure of drug in presence of differentsolubilizing agents and to interpret the probable mechanism of solubilization, UV spectralstudies of indomethacin was performed. (Figs. 2,3,4,5,6,7,8,9,10,11 and 12) [22-26].


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Fig. 2. UV spectra of Indomethacin in water

Fig. 3. UV spectra of Indomethacin in Glycerin


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Fig. 4. UV spectra of Indomethacin in Nicotinamide

Fig. 5. UV spectra of Indomethacin in PEG 200


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Fig. 8. UV spectra of Indomethacin in Propylene Glycol



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Fig. 10. UV spectra of Indomethacin in Sodium Benzoate

Fig. 11. UV spectra of Indomethacin in sodium citrate


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Fig. 12. UV spectra of indomethacin in Urea

2.2.6.2 Fourier transform infrared (FTIR) spectral studies

FTIR spectra were obtained by means of a FTIR spectrophotometer (FTIR – 8300S,Shimadzu, Japan). The samples were prepared by mixing of drug and potassium bromide in1:100 ratio and measurements were attempted over the range of 400–4000 cm-1 (Figs. 13and 14) [22,26].

Fig. 13. FTIR spectrum of indomethacin pure drug


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Fig. 14. FTIR spectrum of indomethacin with all excipients

3. FORMULATION OF AQUEOUS INJECTION

3.1 Preparation of Aseptic Area

The walls and floor of aseptic room were thoroughly washed with water and then disinfectedby mopping with 2.5% v/v Dettol (Reckitt Benckiser India Ltd., Kolkata, India) solution [23-25)]. The bench was cleaned with 70% v/v isopropyl alcohol which was also sprayed in theroom. The aseptic room was fumigated using a mixture of formaldehyde and potassiumpermanganate and the UV lights were switched on for 30 min prior to formulation ofinjections and the filling of injections into vials [23-27].

3.2 Treatment of Packing Material

Amber color glass vials of 2 ml capacity were washed several times with water then finallyrinsed with distilled water. All these vials were placed in an inverted position and sterilized bydry heat in an oven at 160 ºC for 2 h. Rubber stoppers used for plugging the vials were firstshaken in 0.2% liquid detergent solution for 2 h, then washed several times with water toremove any detergent residue and finally rinsed with distilled water. These stoppers weresterilized by autoclaving at 121 ºC and 15 lbs pressure for 15 min. Finally, the stoppers wererinsed with freshly prepared sterile distilled water and dried in vacuum oven under asepticconditions [23,26-28].

3.3 Preparation of Aqueous Injection

On the basis of solubility data obtained from the final blends of mixed solvent, formulation ofaqueous injection of indomethacin was done using mixed solvent system ‘F10’. Thisformulation contained 12.5 mg/ml indomethacin in mixed solvent system ‘F10’ (10% Sodium


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benzoate, 5% sodium citrate, 25% w/v solvent system ‘S’). Sodium bisulfite (0.1% w/v) wasadded as an antioxidant. Other additives like chelating agent and buffering agent were notincluded in these formulations as they might lead to change in the solubility behavior andupset the basic solubility enhancement ratio. [23-27]

For the preparation of aqueous injection of indomethacin, 45 ml of solvent system ‘F10’ wasplaced in 50 ml volumetric flask, weighed amount of indomethacin and 0.1% w/v sodiumbisulfite were added and shaken for 1 hour to ensure complete dissolution. pH of the solutionwas adjusted to 6-7.5 with 0.1 N HCl and 0.1 N NaOH solution and volume was made up to50 ml. These solutions were filtered through 0.45 µ membrane filter (Pall Corporation, USA).The solutions were analyzed spectrophotometrically at 320 nm for drug content after suitabledilutions taking water for injection as blank [23-27].

3.4 Aseptic Filtration and Packaging

The aqueous injection of indomethacin was sterilized by filtration through 0.2 µ disposablemembrane filter fitted in a holder of 5 ml glass syringe and the pressure on the piston wasadjusted. After filtration, the preparation was packed by the sterilized air tight rubber closureand labeled. The final packed vials were sterilized by autoclaving at 15 lbs/sq. inch (121ºC)for 15 min [24-28].

4. CHARACTERIZATION OF AQUEOUS INJECTION

4.1 Stability Study

4.1.1 Physical stability studies

The sealed or packed vials of the aqueous injections were visually inspected each day for 30days against black and white backgrounds for changes in color and turbidity on storage(room temperature, 5ºC±3ºC in refrigerator, and 40 ºC/75% RH in thermostatically controlledovens) [26,30].

4.1.2 Chemical stability studies

The injection formulations were subjected to exhaustive chemical stability studies at5ºC±3ºC in a refrigerator, room temperature and 40ºC±2ºC/75% RH in thermostaticallycontrolled ovens for a period of 30 days. The formulations were analyzedspectrophotometrically initially and at particular intervals to calculate the drug content. Thepercent residual drug for each injection formulation at different time intervals as well as atdifferent temperatures was calculated considering the initial drug content for eachformulation to be 100% (Table 6). From the chemical stability data, the shelf life offormulation was calculated. [25-27,30].

5. RESULTS AND DISCUSSION

5.1 Estimation of Indomethacin in Distilled Water

Results of equilibrium solubility showed that indomethacin has very limited solubility indistilled water (0.0464 mg/ml) which is well below the target solution concentration of 1mg/ml [23,26].


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5.2 Influence of pH on Solubility

Saturated solutions of drug were studied for pH dependent solubility and stability at roomtemperature and analyzed for drug content. Results show that indomethacin has moresolubility in alkaline pH. This may be due to the presence of carbonyl and carboxylic acidfunctional groups on indomethacin which render it acidic. Enhancement in solubility wasfound 80 folds at pH 10 [22, 26, 31].

One of the major factors responsible for dissolution of an organic compound is its ability todissociate into ionic species, which depends on the pH of the media and Percentage ionizedand hence increases solubility due to increase in pH value [32]. Drug was stable at all pHrange. The drug content was found to be more than 98% after stability duration of 30 days(Table 1)

5.3 Solubility Determination in Hydrotropic Agents and Co-solvents

The hydrotropes selected for the study (nicotinamide, sodium benzoate, urea and sodiumcitrate) possess hydrophobic center which can interact due to large surface area and amobile electron cloud. These sites are available for non-bonded and Van der Waalsinteraction with water and drug. Water molecules join together to form cluster. Forsolubilization, the ionized hydrotropes break this association and use the ion–dipoles ofwater for solvation [33].

The solubility of indomethacin in different hydrotropic agents and co-solvents is shown inTable 2. The maximum solubility was observed in 40 % sodium benzoate with enhancementratio of 665.021. Solubility enhancement for 40 % hydrotropic solution could be ranked indecreasing order as Sodium benzoate> nicotinamide> urea> sodium citrate and thesolubility enhancement ratio 665.021 > 569.353 >186.034 >15.172 respectively. Solubilityenhancement for co-solvents could be ranked as PEG 600 > PEG 6000 > PEG 400 >Glycerine> PEG 200> Propylene Glycol. The use of hydrotrope combinations yields higherindomethacin solubility than that of the single hydrotrope. The higher the hydrotropeconcentration in the solution the more drug could be solubilized [23].

On increasing the concentration of solubilizers, the solubility of indomethacin increases butthis leads to enhanced toxic effect of the solubilizing agents. Investigations reveal thatincorporation of hydrotropes in combination into cosolvent solution increases drug solubilitybetter than cosolvent solution alone. Hence, instead of using a single solubilizer in largerconcentration for development of dosage form, a combination of solubilizers in comparativelysmaller concentrations increase solubility and the associated toxic effects can be reduced[26].

5.4 Solubility in Mixed Solvents

Mixed solvent system was prepared to determine solubility and about 100 to 400 foldincrease in solubility was seen which may be due to the additive/synergistic effect of themixed solvents. Combination of 10% sodium benzoate, 5% sodium citrate and 25% ofcosolvent “S” increase solubility by 430 folds, which is well beyond desired concentrationshown in Table 3. The structures of drugs and hydrotropes with different centers of differentelectro negativity might be responsible for the intermolecular hydrogen bonding andelectrostatic attraction. Nicotinamide formed hydrogen bonding with oxygen of the carbonyl


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groups of the drug and lowered the wave number of its carbonyl stretch. This impartedaqueous solubility through various hydrogen bonding centers on hetero atoms with non-bonded electron pair on it. Sodium ion from sodium benzoate formed ion–dipole bond withcarbonyl group of indomethacin. Further, London forces between aromatic rings (non-polarparts) and hydrogen bonding between polar parts also play a role in imparting aqueoussolubility enhancement of indomethacin by sodium benzoate. Hydrogen bonding betweenthe amide group of urea and various negative centers of indomethacin molecule seems toenhance aqueous solubility to indomethacin. Electronegative corboxylate ion and hydroxylgroup of sodium citrate increase solubility of drug. By disrupting self-association of water,cosolvents reduce the squeezing out of non-polar hydrophobic compounds and increasesolubility. Most of the cosolvents have hydrogen bond donor and/or acceptor groups as wellas small hydrocarbon regions. Hydrotropic agents produce weak ionic interaction, whichindicates that their hydrophilic hydrogen bonding groups ensure water miscibility to a greaterextent [26].

5.5 Properties of Mixed Solvent Solutions

The solution properties of mixed solvents were studied for selected blends F7-F8 and F10-F12 which showed solubility enhancement ratio upto 300-400 fold (Other blends were notselected due to less solubility enhancement ratio). Results reveal that pH of the formulationsis less alkaline so it would be less irritant at the site of application. Viscosity of solutionsincreased as increasing concentration of hydrotropes leading to the formation of aggregates,change in specific gravity and surface tension [34]. Change in specific gravity might occurdue to increase in partial molal volume upon aggregation [31]. The decrease in surfacetension was due to self association as hydrotropes are not surface active agent [22]. Resultsshowed in Table 4.

5.6 UV spectral Studies

In case of indomethacin-mixed solvent system, a minor shift in λmax (320 ± 0.5 nm) wasobserved, which may be due to electronic changes in the structure of drug molecules. This isnot indicative of any complex formation between drug and hydrotrope molecules, as thecomplex formation can be evidenced by formation of new chromophores (by merging of twopeaks to generate a common peak). Small additional peaks of solubilizers and cosolventwere also observed in UV spectra which indicates that there is no interference ofsolubilizer/cosolvents with the absorbance of the drug (Figs. 2-12).

5.7 Fourier Transform Infrared (FTIR) Spectral Studies

To check the integrity of the drug in the formulation an IR spectral study was carried out. Thespectra obtained from IR studies (at wavelength 4000 cm-1 to 400 cm-1) showed that thereare neither major shifts nor any loss of functional peaks between the spectra of drug andpolymer. IR of drug with all solubilizers was compared with that of the pure drug to seewhether there was any change in the structure or interaction with the polymers. Thesolubilized product with mixed solvent shows the two carbonyl stretches of indomethacinshifted to lower wave number than the carbonyl stretch of pure compound, that is 1716.65and 1691.57 to 1670.35 and 1595.13. This proves hydrogen bonding and London forcebetween aromatic rings which impart aqueous solubility to drug. The IR spectrum forindomethacin shows peaks at 3,342.6 and 1,670.5 cm −1, corresponding to carboxylic O−Hand C=O stretch respectively. The O–H stretching frequency of the carboxylic acid group of


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indomethacin observed at around 3,350.5. Pattern of C=O stretch vibrations is typicallyobserved in the range of 1600-1750 cm-1. Peak at 1691 cm-1 is assigned to benzoylvibration. Peak at around 754 cm -1 represent halogen (below 1000) and aromatic overtonewas observed at 1000-2000 cm -1 (Figs. 13 and 14 ) [22, 26].

5.8 Physical Stability Studies

Blend F10 was selected and used to develop aqueous parenteral formulation owing to itssuperior and synergistic effect on solubility of indomethacin. Formulated aqueous injectionwas subjected to physical stability testing at 5ºC±3ºC, at room temperature and at 40ºC/75%RH. Results of the physical stability study of formulation F10 showed that it remainunchanged in respect of pH and color. No turbidity or precipitate formation was observed atdifferent storage conditions, showing appreciable physical stability (Table 5) [23, 26].

Table 5. Physical stability data of formulation F10

Condition Physical stability parameterpH Color Precipitation

Initial After 30days



Refrigeration(5ºC±3ºC)

7.08 7.09 Colorless Colorless No ppt. No ppt.

Room Temperature 7.08 7.14 Colorless Colorless No ppt. No ppt.40ºC/75%RH 7.08 7.17 Colorless Colorless No ppt. No ppt.

5.9 Chemical Stability Studies

The indomethacin content was also found to be within the pharmacopoeial limits in all theformulations. The data on chemical stability at different temperatures and time intervals areshown in Table 6. The degradation of indomethacin follows first order kinetics. The timerequired for the 10% degradation of drug for formulations was calculated. Results show thatthe prepared formulation F10 had a shelf life of 7-8 months at room temperature [25,27-30].

Table 6. Chemical Stability Data of Formulation F10

FormulationCode

Temperature Concentration* mg/vials Degradation0 Day 7 Day 15 Day 30 Day

F10 5ºC±3ºC 49.82±0.004

49.70±0.011

49.52±0.007

49.42±0.009

0.803%

25±2ºC 49.82±0.004

49.64±0.013

49.47±0.017

49.25±0.011

1.145%

40ºC±2ºC/75% RH

49.82±0.004

49.53±0.009

49.29±0.014

49.05±0.014

1.54%


6. CONCLUSION

The present investigation showed the possibility of aqueous injection of poorly water solubledrugs using combination of various solubilizers and hydrotropic agents which acts


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synergistically at very low individual concentrations. Hence, toxicity and safety related issuesmay not raise concern and would suggest their adaptability for large scale manufacturing.

Stable aqueous injection of indomethacin and other poorly water soluble drug could besuccessfully developed using the concept of mixed-solvency. These combinations eliminatethe need for including any surfactant in the parenteral dosage formulation with the potentialadvantage of less associated toxicity. The amount of individual solubilizers required toincrease the measurable solubility may be very high which sometimes shows the toxicity.Therefore, the use of mixed solvents (blends of enumerate solubilizers) which arephysiologically compatible and often acts synergistically will improve the solubility andreduce the risk of toxicity.

The proposed technique is economical, convenient and safe. Thus, this study opens thechance of preparing aqueous formulations of poorly-water soluble drugs and the chemicalstability of drug remains unaffected. Mixed solvency approach produce a physical stableformulation with low level of cosolvents to the patient, thus reducing or eliminating the effectof cosolvent toxicity and erythrocyte damage.

The present investigation focuses on the application of mixed-solvency concept todiscourage the use of organic solvents in formulation and analysis to a great extent.

Thus, it can be concluded that with the carefully designed experimental technique, solubilityof poorly water soluble drug can be improved using “mixed solvency” approach. Theapplication of mixed solvency approach in the development of formulations shall prove aboon for pharmaceutical industries because the quantities of water soluble solubilizerspresent in the blends can be selected at safe level (well below their toxic levels) for a modestincrease in solubility of a water-insoluble drug.

CONSENT

Not applicable.

ETHICAL APPROVAL

Not applicable.

ACKNOWLEDGEMENTS

The authors would like to acknowledge Neon Laboratories, Mumbai, India for providing giftsample of Indomethacin and to the School of Pharmacy DAVV, Indore and College ofPharmacy, IPS Academy, Indore (India) for providing necessary facilities for the work.

COMPETING INTERESTS

Authors have declared that no competing interests exist.

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Peer-review history:The peer review history for this paper can be accessed here:

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